Temperature effects of bifacial modules

Abstract

In this paper we show the results from indoor and outdoor measurements on solar cells and modules, manufactured with different bifacial and monofacial cell architectures and encapsulated in different configurations. Reflection/transmission, IV and IQE spectra of single-cell laminates were measured and used to determine the energy spectra for all heat loss and absorption processes, including thermalisation, recombination, entropy generation, parasitic absorption and electrical power generation. From these spectra, the effective heat input was calculated for front, rear and combined irradiance. The power output, bifacial gain and module operating temperature were monitored of single-cell laminates exposed to indoor irradiance as well as of full-size modules installed on our rooftop. We have found that the effective heat input for bifacial glass-glass modules is increasingly larger with increasing rear irradiance compared to monofacial modules. Measured temperatures of rooftop-installed modules strongly indicate that the effective heat transfer coefficient of glass-glass modules is higher than that of white back sheet modules. The observed combined effect of heat input and heat transfer is that only at rear irradiance fractions beyond 15% the additional heat input can cause the bifacial modules to be hotter than their monofacial counterpart, but the energy yield is still much higher due to the large bifacial gain. In the case of moderate albedo, the bifacial energy gain is not accompanied by a higher temperature of the bifacial module compared to the monofacial module.